Liquid crystal display (LCD) devices have been widely used because they are characteristically thin, power-saving, and nonradiative. LCD devices currently on the market are mainly backlight ones which each usually comprises an LCD panel and a backlight module. The LCD panel is provided with two glass substrates and a liquid crystal material sandwiched between the two glass substrates. By applying a drive voltage on the two glass substrates, directions of molecules in the liquid crystal material are controlled and light from the backlight module can thus be reflected to produce images.
Response time of liquid crystals is a significant parameter for evaluating the quality of an LCD device. According ISO13406-2, when a pixel changes from white to black, the voltage on the pixel electrode changes from zero to its maximum value, and driven by this maximum voltage, liquid crystal molecules orient themselves quickly to new positions (the duration of this process is called rise time); and when a pixel changes from black to white, the voltage on the pixel electrode is cut off, and liquid crystal molecules return to their original positions before the voltage was applied (the duration of this process is called fall time). The response time of liquid crystal molecules is the sum of the rise time and the fall time. From the perspective of grayscale, response time is actually the deflection speed of liquid crystal molecules. There are generally three methods to enhance the deflection speed of liquid crystal molecules.
1. The first method is to increase the drive voltage. Deflection speed of liquid crystals is related to the voltage. The higher the voltage is, the larger the deflection speed of liquid crystal molecules is.
2. The second method is to change the initial state of liquid crystal molecules. This is in fact to enable the liquid crystal molecules to be in an unstable state, so that the liquid crystal molecules can react immediately in response to a stimulus. This method can reduce response time but it cannot be used very freely because the liquid crystal molecules cannot be too unstable, otherwise it would be difficult to control them.
3. The third method is to reduce the viscosity of liquid crystal material. The thicker the liquid crystal material is, the harder it is to drive liquid crystal molecules. If the liquid crystal material is diluted, it becomes easier to drive the liquid crystal molecules to deflect, as a consequence of which the response time is rendered shorter. However, dilution of the liquid crystal material may affect its ability to control light. The response time is reduced, but the cost is high. The less viscous the liquid crystal material is, the lighter the color of images is; and as a result, details of the images become obscure and meanwhile there might be slight light leakage. This is also the reason why LG used grayscale technology merely in its super in-plane switching (S-IPS) panels.
Because of the disadvantages of the above method 2 and method 3, reduction of grayscale response time currently mainly relies on voltage increase, which method is referred to by panel manufacturers (i.e., AU Optronics) as overdrive (OD) technology.
Existing overdrive methods and modes are all based on LCD devices with an RBG three-color display system. It is therefore desirable to provide an improved overdrive system with respect to a four-color display system such as an RGBW/RGBY system.
At present, in a display device with an LCD panel or an organic light-emitting diode (OLED) panel, a pixel is mostly formed by a red (R) sub-pixel, a green (G) sub-pixel, and a blue (B) sub-pixel. By regulating the grayscale value of each sub-pixel and blending colors of the sub-pixels, desired colors are achieved to display color images. With the development of information technologies, people are requiring more of display panels on properties such as high light transmittance, low power consumption, and image quality. An existing display method by blending RGB three-primary colors of light performs low in light transmittance and blending efficiency. This leads to large power consumption of display panels, and thus is not conducive to product optimization of display panels. In view of this, it was proposed to form a pixel with four sub-pixels: a red (R) sub-pixel, a green (G) sub-pixel, a blue (B) sub-pixel, and a fourth sub-pixel, so as to improve the display quality of RGB display panels.
The additional fourth sub-pixel is usually a white (W) sub-pixel, and a pixel is formed by an R sub-pixel, a G sub-pixel, a B sub-pixel, and a W sub-pixel. A display device with an RGBW display panel has to convert inputted primary RGB data into RGBW data, so that the RGBW display panel can be driven to achieve display. Whereas according to existing methods by which primary RGB data is converted into RGBW data, sub-pixels in a pixel has to satisfy the relational expression W=R+G+B.
FIG. 1 is a transmittance spectrogram of a W sub-pixel according to the prior art. FIG. 2 is a transmittance spectrogram of R, G, B sub-pixels according to the prior art. Referring to FIGS. 1 and 2, in practice, it is hard to satisfy the relational expression W=R+G+B because backlight (e.g., blue light) produced by a backlight module travels directly through the W sub-pixel (which is usually made of a transparent photoresist) In addition, light emitted from the W sub-pixel is closely similar to light emitted from the B sub-pixel. Under this circumstance, if the RGBW display panel displays white, the light emitted from the W sub-pixel and the light emitted from the B sub-pixel may cause it incapable of covering a normal white spectrum scope, and further cause an unusual chromatic value of white.